David William Webster posted the following to the ImageJ mailing list.

For those who haven’t tried to use the macro debug mode that is part of the
imageJ text editor, here are brief descriptions of each option.

Debug – Enters debug mode and opens a debug record window. The window
initially displays the memory usage, number of open images and the active
image’s title. The debugger is set to the first executable line of code. You
must be in debug mode for any of the following to work

Step – Steps through each line of code sequentially and displays the variable
names and values.

Trace - Runs the macro and displays variable names and values as they
are encountered.

Fast Trace - Same as above, but faster.

Run - Runs the macro the same as Macros/Run Macro command.

Run to Insertion Point - Runs macro to a point defined by left clicking the
mouse on a specific executable line of code.